A piston compressor of this kind is known, for example, from U.S. Pat. No. 4,478,559. The driving rod is formed by a connecting rod, which is provided with a longitudinal bore, through which the lubricating oil is conveyed from a crankshaft-side end of the connecting rod to the piston pin. In the piston pin is provided a radial bore, through which the lubricating oil reaches the longitudinal bore. In the longitudinal bore the lubricating oil is pressed upward and thus reaches the lubrication groove, which extends on the outside of the piston. Here the oil supports the lubrication of the working surfaces of cylinder and piston and the sealing between cylinder and piston.
U.S. Pat. No. 5,118,263 shows a further hermetically enclosed refrigerant compressor, which has on the outside of the cylindrical surface of the piston pin a circumferential lubrication groove, which is connected with the opening of a longitudinal bore in the connecting rod and serves the purpose of supplying lubricating oil to the pin bearing formed in the piston-side connecting rod eye. Subsequently, the oil leaving the pin bearing reaches the lubrication groove on the outside of the piston, there supporting the lubrication of the working surfaces of cylinder and piston and contributing to an improved sealing between cylinder and piston. However, the amount of oil reaching the cylinder in this way is relatively small. For this reason, additional oil is supplied directly, however without pressure, through an opening formed on the upper side of the cylinder block, said opening ending in the area of the circumferential piston groove. A lubrication groove in the piston pin for distributing the oil weakens the creation of a stable oil film in the pin bearing.
In many cases, the lubrication groove formed in the outer cylindrical surface of the piston jacket is not always completely filled with oil, but a certain amount of gas remains, particularly in the upper area of the lubrication groove. Here, compressed refrigerant gas from the compression chamber of the cylinder can penetrate into the lubrication groove through the gap between piston and cylinder. Through a ventilation opening formed in the piston, the resulting gas-oil mixture is pressed into the inside volume of the compressor housing, which causes an undesirable noise generation. Further, the efficiency of the compressor is decreased, as compressed refrigerant gas is lost.
Further noises occur in that the high pressure of the compressed refrigerant gas causes a share of the gas-oil mixture to be pressed back into the drive system through the oil supply system, that is, the longitudinal bore in the connecting rod, from where it can be pressed out through openings in the crankshaft. Additionally, this may have a negative effect on the sufficient lubrication of the bearing, that is, the crankshaft side pin bearing.
The invention is based on the task of improving the lubrication.